Liquid crystal display device and driving method thereof

ABSTRACT

A liquid crystal display device includes a group of first signal lines ( . . . , Sm−1, Sm, Sm+1, . . . ) arranged in parallel, a group of second signal lines ( . . . , Gn−1, Gn, Gn+1, . . . ) and a group of auxiliary capacity wirings ( . . . , Csn−1, Csn, Csn+1, . . . ) alternately arranged one by one in parallel so as to intersect with the group of the first signal lines, a plurality of pixel electrodes arranged in a pixel region, an auxiliary electrode connected to each of the pixel electrodes, and a TFT element corresponding to each of the pixel electrodes. The auxiliary electrode has a portion forming a capacitor by overlapping with auxiliary capacity wiring Csn and a portion forming a capacitor by overlapping with second signal line Gn−1.

This nonprovisional application is based on Japanese Patent ApplicationsNos. 2003-137223 and 2004-130622 filed with the Japan Patent Office onMay 15, 2003 and Apr. 27, 2004, respectively, the entire contents ofwhich are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an active matrix liquid crystal displaydevice widely used for OA or AV equipment, and a driving method thereof.

2. Description of the Background Art

A liquid crystal display device generally has a structure such that, aliquid crystal layer is sandwiched between an opposed electrode and apixel electrode. In particular, in an active matrix liquid crystaldisplay device, numbers of pixel electrodes are arranged in a matrix. Todisplay an image in the active matrix liquid crystal display device, apicture signal is successively provided to the numbers of pixelelectrodes arranged two-dimensionally in a matrix, on a column-by-columnbasis. Hereinafter, this process is referred to as “scanning”. At atiming when the scanning reaches a certain column of the pixelelectrodes, a voltage as a picture signal is applied simultaneously toall of the pixel electrodes belonging to the column, and a potentialdifference held at that time in each pixel electrode for the opposedelectrode must be kept to a sufficient degree until next scanning comesto the column of the pixel electrodes. As a capacitance (which is alsoreferred to as “a liquid crystal capacity”, generally indicated with“Clc”) resulting from a liquid crystal between the pixel electrode andthe opposed electrode is usually not sufficient, a technique is known togive the pixel electrode an auxiliary capacity (generally indicated with“Cs”) to help charge keeping of the pixel electrode. More specifically,to give the auxiliary capacity, it is contemplated that a portion of thepixel electrode is arranged so as to overlap with another wiring or thelike with interposed dielectric.

Techniques disclosed in Japanese Patent Laying-Open No. 10-274783 andNo. 7-311390 are examples of conventional techniques regarding theauxiliary capacity. In these techniques, one pixel region is dividedinto a plurality of pixel electrodes, and one of the pixel electrodeshas a portion overlapping with capacity wiring to achieve an auxiliarycapacity as a so-called Cs on Common, while another pixel electrode hasa portion overlapping with a gate signal line for an adjacent pixel toachieve an auxiliary capacity as a so-called Cs on Gate. Each of thedivided pixel electrodes has a TFT (Thin Film Transistor) element fordriving. An object of the techniques in Japanese Patent Laying-Open No.10-274783 and No. 7-311390 is to improve a visual angle characteristicof a liquid crystal display device by providing a plurality of regionshaving different auxiliary capacity components within one pixel.

Other relational conventional techniques include Japanese PatentLaying-Open No. 7-218930 and No. 9-15622 as examples of Cs on Common,and Japanese Patent Laying-Open No. 8-146464 and No. 2000-227611 asexamples of Cs on Gate.

Generally, auxiliary capacity Cs is achieved with the aforementioned twosystems, Cs on Gate and Cs on Common.

FIG. 17 shows a circuit diagram of Cs on Gate. Cs on Gate means that theauxiliary capacity is retained between a pixel electrode or an auxiliaryelectrode having the same potential as the pixel electrode and a gatesignal line Gn−1 for an adjacent pixel region. A portion enclosed withdotted line in FIG. 17 indicates a position in the circuit constructionoccupied with the pixel electrode or the auxiliary electrode having thesame potential as the pixel electrode.

FIG. 18 shows a circuit diagram of Cs on Common. Cs on Common means thatthe auxiliary capacity is retained between a pixel electrode or anauxiliary electrode having the same potential as the pixel electrode andauxiliary capacity wiring Cs. Auxiliary capacity wiring Cs is wiringarranged between gate signal lines to achieve Cs on Common structure.Thus, the gate signal lines and auxiliary capacity wirings arealternately arranged one by one.

Both of the two systems Cs on Gate and Cs on Common have respectivemerits and demerits, and are selected corresponding to specific needs.One of the merits of Cs on Gate is that, there is no need to arrange anew capacity line, as a gate signal line of an adjacent pixel of eachpixel is used as wiring to achieve the auxiliary capacity. In addition,as an arrangement of an additional capacity line is not required, anaperture ratio is not decreased. One of the demerits, however, is that,as a load for auxiliary capacity Cs is applied to the gate signal lineof the adjacent pixel, power supply efficiency during a gate-off time (astate of a voltage being VGL) becomes lower and a current consumption isincreased. On the other hand, one of the merits of Cs on Common is asmall current consumption. One of the demerits is a decreased apertureratio, as the auxiliary capacity wiring must be additionally arrangedonly for achieving the auxiliary capacity.

As a liquid crystal has permittivity anisotropy, liquid crystal capacityClc varies depending on a voltage applied to the liquid crystal. Thus, adirect current component originally held by a potential of the pixelelectrode changes with the picture signal. As a result, an undesireddirect current component is newly generated. When a direct currentvoltage is applied to the liquid crystal by the direct current componentgenerated as such, a flicker (flickering or shaking of a screen) occurs.In addition, if the direct current component is generated, an afterimage is formed, which may be resulting from formation of an electricdouble layer on an interface between an alignment layer and the liquidcrystal. Furthermore, a response property of a picture is known to bedegraded because liquid crystal capacity Clc changes with the appliedvoltage.

Sufficiently large auxiliary capacity Cs can suppress theabove-described problems caused by a variation in liquid crystalcapacity Clc and can enhance performance of the liquid crystal displaydevice. The auxiliary capacity, however, is not sufficiently large inany of the techniques in aforementioned six references.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a liquid crystaldisplay device which can ensure an auxiliary capacity of a sufficientsize, and a driving method thereof.

To attain the above-described object, one aspect of a liquid crystaldisplay device according to the present invention includes a group offirst signal lines arranged in parallel, a group of second signal linesand a group of auxiliary capacity wirings alternately arranged one byone in parallel so as to intersect with the group of the first signallines, a plurality of switching elements arranged corresponding tointersection points of the first signal lines and the second signallines, a plurality of auxiliary electrodes connected to the plurality ofswitching elements, and a pixel electrode formed on the auxiliaryelectrode and electrically connected to the auxiliary electrode, whereinthe auxiliary electrode has a portion forming a capacitor by overlappingwith the auxiliary capacity wiring and a portion forming a capacitor byoverlapping with the second signal line. By adopting this construction,as both of a portion forming an auxiliary capacity as Cs on Gate byoverlapping of the auxiliary electrode having the same potential as thepixel electrode with a gate signal line, and a portion forming anauxiliary capacity as Cs on Common by overlapping of the auxiliaryelectrode with the auxiliary capacity wiring are present, the auxiliarycapacity can increase.

To attain the above-described object, another aspect of the liquidcrystal display device according to the present invention includes agroup of first signal lines arranged in parallel, a group of secondsignal lines and a group of auxiliary capacity wirings alternatelyarranged one by one in parallel so as to intersect with the group of thefirst signal lines, a plurality of pixel electrodes arranged in a pixelregion defined as each region enclosed with two of the group of thefirst signal lines which are adjacent with each other and two of thegroup of the second signal lines which are adjacent with each other, anauxiliary electrode connected to each of the pixel electrodes, and athin film transistor corresponding to each of the pixel electrodes,wherein the thin film transistor has one side of a source and a drainconnected to the first signal line, the other side connected to theauxiliary electrode, and a gate side connected to the second signalline, and the auxiliary electrode has a portion forming a capacitor byoverlapping with the auxiliary capacity wiring and a portion forming acapacitor by overlapping with the second signal line. By adopting thisconstruction, as both of a portion forming an auxiliary capacity as Cson Gate by overlapping of the auxiliary electrode having the samepotential as the pixel electrode with a gate signal line, and a portionforming an auxiliary capacity as Cs on Common by overlapping of theauxiliary electrode with the auxiliary capacity wiring are present, theauxiliary capacity can increase.

In the present invention, it is preferable that each of the plurality ofpixel electrodes includes the corresponding auxiliary electrode and thethin film transistor, and one of the group of the second signal lineslocated in an end position of one side has a portion forming a capacitorby overlapping with the auxiliary electrode and is not connected to anyof the thin film transistor. By adopting this construction, when thegroup of the second signal lines is a group of gate signal lines, forexample, the construction has a dummy gate signal line, and thus theauxiliary capacity can increase even in one of pixels for display whichis located in an end position.

In the present invention, it is preferable that each of the pixelelectrodes includes the corresponding auxiliary electrode and the thinfilm transistor, and a picture signal is not applied to the pixelelectrode located between two of the group of the second signal lines infirst and second positions from an end of one side. By adopting thisconstruction, the construction has a dummy pixel electrode, and thus theauxiliary capacity can increase even in one of pixels for display whichis located in an end position.

To attain the above-described object, in a driving method of a liquidcrystal display device according to the present invention, in theabove-described liquid crystal display device, when a group of secondsignal lines are indicated with G0, G1, G2, . . . , Gp in order ofarrangement position, a picture signal to be displayed is successivelyapplied to G1 to Gp in one vertical period, and a constant potential isapplied to G0. By adopting this method, the liquid crystal displaydevice having a construction including a dummy gate signal line and anincreased auxiliary capacity can be driven efficiently.

To attain the above-described object, in a driving method of a liquidcrystal display device according to the present invention, in theabove-described liquid crystal display device, when a column of thepixel electrodes located between two of the group of the second signallines in first and second positions from an end of one side is made tobe a dummy pixel electrode column and the other columns of the pixelelectrodes are made to be active pixel electrode columns, the drivingmethod comprises the steps of selecting a column one by one in order ofarrangement position over all of the active pixel electrode columns,providing a potential corresponding to content of a picture to bedisplayed to the selected one column of the pixel electrodes, providinga constant potential to the other columns of the pixel electrodes, andrepeating such scanning from one end to the other end of an arrangementof the active pixel electrode columns, while continuously providing theconstant potential to the dummy pixel electrode. By adopting thismethod, the liquid crystal display device having a constructionincluding a dummy pixel electrode and an increased auxiliary capacitycan be driven efficiently.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged plan view corresponding to one pixel of a liquidcrystal display device in a first embodiment according to the presentinvention.

FIG. 2 is a schematic cross-sectional view of the liquid crystal displaydevice in the first embodiment according to the present invention.

FIG. 3 is a circuit diagram corresponding to one pixel of the liquidcrystal display device in the first embodiment according to the presentinvention.

FIG. 4 is a schematic cross-sectional view of a liquid crystal displaydevice in a second embodiment according to the present invention.

FIG. 5 is a circuit diagram of a region near a dummy gate signal line inan example of the liquid crystal display device in the first or secondembodiment according to the present invention including the dummy gatesignal line.

FIG. 6 is a time chart showing signal application states in gate signallines Gn and Gn+1 of the liquid crystal display device in the first orsecond embodiment according to the present invention.

FIG. 7 is a time chart showing signal application states in gate signallines G0 and G1 of the liquid crystal display device in the first orsecond embodiment according to the present invention.

FIG. 8 is a circuit diagram of a region near a dummy pixel electrode inan example of the liquid crystal display device in the first or secondembodiment according to the present invention including the dummy pixelelectrode.

FIG. 9 is a first diagram to describe how positive and negative signalsare alternately applied to a pixel electrode.

FIG. 10 is a conceptual diagram of a relation between a screen anddrivers in a general single-bank drive situation.

FIG. 11 is a second diagram to describe how positive and negativesignals are alternately applied to the pixel electrode.

FIG. 12 is a conceptual diagram showing a variation in a potential of agate electrode, which is assumed in a third embodiment according to thepresent invention.

FIG. 13 is a circuit diagram showing connections of Csg, Clc and Cscomto a TFT element in one pixel, which is assumed in the third embodimentaccording to the present invention.

FIG. 14 is a circuit diagram of a simulation model assumed in the thirdembodiment according to the present invention.

FIG. 15 is a graph showing a result of the simulation performed in thethird embodiment according to the present invention.

FIG. 16 is a conceptual diagram of a relation between a screen anddrivers in a general dual-bank drive situation.

FIG. 17 is a circuit diagram corresponding to one pixel of a liquidcrystal display device adopting a Cs on Gate structure according to aprior art.

FIG. 18 is a circuit diagram corresponding to one pixel of a liquidcrystal display device adopting a Cs on Common structure according to aprior art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As the techniques disclosed in aforementioned Japanese PatentLaying-Open No. 10-274783 and No. 7-311390 are to achieve an auxiliarycapacity with either Cs on Gate or Cs on Common for each of pixelelectrodes divided in a plurality, only one of Cs on Gate and Cs onCommon can be used for one pixel electrode and, as a result, theauxiliary capacity is not sufficiently large. It is to be noted that, anobject of the techniques disclosed in aforementioned Japanese PatentLaying-Open No. 10-274783 and No. 7-311390 is to improve the visualangle characteristic and not to increase the auxiliary capacity, andthus a viewpoint of increasing the auxiliary capacity is not consideredat all.

In contrast, inventors of the present invention focused attention on theobject of increasing the auxiliary capacity, which is absolutelydifferent from that of prior arts, and attained the present invention toachieve an increased auxiliary capacity.

First Embodiment

A liquid crystal display device in a first embodiment according to thepresent invention will now be described referring to FIGS. 1-3. FIG. 1is an enlarged plan view of one pixel region of the liquid crystaldisplay device. The liquid crystal display device includes a group ofsource signal lines ( . . . , Sm−1, Sm, Sm+1, . . . ) as first signallines. It also includes a group of gate signal lines ( . . . , Gn−1, Gn,Gn+1, . . . ) as second signal lines and a group of auxiliary capacitywirings ( . . . , Csn−1, Csn, Csn+1, . . . ) arranged in parallel so asto intersect with the group of the first signal lines. The gate signallines and the auxiliary capacity wirings are alternately arranged one byone in parallel.

One pixel region is defined as a region enclosed with two of the groupof the source signal lines which are adjacent with each other, that is,Sm and Sm+1, and two of the group of the gate signal lines which areadjacent with each other, that is, Gn−1 and Gn. As pluralities of sourcesignal lines and gate signal lines are arranged, a plurality of pixelregions are defined in a display region of the liquid crystal displaydevice. In each of the pixel regions, a pixel electrode 11 is arrangedso as to cover the pixel region. Only one pixel electrode 11 is shown inFIG. 1. As each of the plurality of pixel regions has the sameconstruction, a structure within one pixel region is described in thefollowing.

Pixel electrode 11 is located on a forward side of a paper surface ascompared with an auxiliary electrode 13. The liquid crystal displaydevice includes auxiliary electrode 13 connected so as to continuouslyhave the same potential as pixel electrode 11, and a thin filmtransistor element (hereinafter referred to as a “TFT element”) 10arranged corresponding to pixel electrode 11. TFT element generally hasthree terminals of source, drain and gate, and in this liquid crystaldisplay device, one side of the source and drain is connected to thefirst signal line, while the other side is connected to the auxiliaryelectrode, and a gate side is connected to the second signal line. Morespecifically, TFT element 10 has a source side connected to sourcesignal line Sm, a drain side connected to auxiliary electrode 13, and agate side connected to gate signal line Gn. One auxiliary electrode 13has both of a portion forming a capacitor by overlapping with auxiliarycapacity wiring Csn and a portion forming a capacitor by overlappingwith gate signal line Gn−1.

FIG. 2 is a schematic cross-sectional view of this construction which iscut along a plane in parallel with the source signal line. FIG. 2 is nota completely realistic cross-sectional view, and partially includesrepresentations for a circuit diagram. It is shown that cross sectionsof gate signal line Gn−1, auxiliary capacity wiring Csn and gate signalline Gn are respectively arranged on a substrate 20. A transparentinsulation film 19 covers the wirings. Auxiliary electrode 13 isarranged on an upper side of transparent insulation film 19. TFT element10 is formed in transparent insulation film 19 with auxiliary electrode13, an electrode extending from the source signal line (not shown inFIG. 2; see FIG. 1) and gate signal line Gn. An upper side of auxiliaryelectrode 13 is covered with a transparent insulation film 18, and pixelelectrode 11 is arranged on an further upper side thereof. Pixelelectrode 11 and auxiliary electrode 13 are electrically connected witheach other by a contact hole 12 (not shown in FIG. 1; see FIG. 2).Therefore, pixel electrode 11 and auxiliary electrode 13 always have thesame potential. A liquid crystal layer 17 is arranged on an upper sideof pixel electrode 11 via an alignment layer (not shown). An opposedelectrode 15 is arranged on an upper side of liquid crystal layer 17,again via an alignment layer (not shown). A black matrix 16 is partlyarranged on an upper side of the opposed electrode. When seentwo-dimensionally, black matrix 16 is arranged in a grid line pattern soas to cover gaps between the adjacent pixel electrodes. Alternatively,it may be formed so as to cover the gate signal lines or the sourcesignal lines to cut off reflected light of outside light at the gatesignal lines or the source signal lines. The pixel electrode and theopposed electrode is formed with a transparent conductive material.

FIG. 3 shows a circuit diagram of this construction. A portion enclosedwith dotted line indicates a position in the circuit constructionoccupied with pixel electrode 11 and auxiliary electrode 13.

In the liquid crystal display device according to this embodiment, bothof a portion forming auxiliary capacity CsG as Cs on Gate by overlappingof auxiliary electrode 13 continuously having the same potential aspixel electrode 11 with gate signal line Gn−1, and a portion formingauxiliary capacity CsC as Cs on Common by overlapping of the auxiliaryelectrode with auxiliary capacity wiring Csn are present, and thus theauxiliary capacity can increase. In this construction, with retaining anaperture ratio as high as a conventional construction only with Cs onCommon, the auxiliary capacity can be made larger as compared with theconstruction only with Cs on Common.

As the auxiliary capacity can be provided from both of Cs on Common andCs on Gate in the present invention, the auxiliary capacity allocated toone pixel will be a sum of the two. Therefore, even when the auxiliarycapacity of each of Cs on Common and Cs on Gate is made smaller to someextent, the auxiliary capacity equal to or larger than that with onlyone of them can be ensured. Considering this point, in the presentinvention, an auxiliary capacity line for forming Cs on Common and agate signal line for forming Cs on Gate can respectively be made thinneras the auxiliary capacity of each of Cs on Common and Cs on Gate is madesmaller. As a result, the problem of decreased aperture ratio, which isone of the demerits of the structure only with Cs on Common, can besolved and the aperture ratio can be sufficiently high. In addition, asthe auxiliary capacity line and the gate signal line can be madethinner, a smaller pixel structure can be formed, which is advantageousto acquire a high definition pixel structure. Furthermore, as theauxiliary capacity can be added by Cs on Common in the presentinvention, a load of Cs on Gate becomes smaller as compared with thestructure only with Cs on Gate, and thus the problem of increased powerconsumption, which is one of the demerits of the structure of Cs onGate, can be suppressed.

Second Embodiment

Though the liquid crystal display device is described in the firstembodiment assuming that it has a so-called SHA (Super High Aperture)structure, in which auxiliary electrode 13 and transparent insulationfilm 18 are interposed between a layer having TFT element 10 arrangedtherein and pixel electrode 11 to increase an aperture ratio, thepresent invention is also applicable to a liquid crystal display devicenot having the SHA structure. Therefore, an example of application ofthe present invention to a liquid crystal display device having non-SHAstructure is described as a liquid crystal display device in a secondembodiment according to the present invention. FIG. 4 shows, similarlyas FIG. 2 of the first embodiment, an example of a schematiccross-sectional view of the liquid crystal display device in thisembodiment. Cross sections of gate signal line Gn−1, auxiliary capacitywiring Csn and gate signal line Gn are respectively arranged onsubstrate 20. Transparent insulation film 19 covers the wirings. Pixelelectrode 11 is arranged on an upper side of transparent insulation film19. TFT element 10 is formed in transparent insulation film 19 with aportion of pixel electrode 11, an electrode extending from the sourcesignal line (not shown) and gate signal line Gn. A structure of an upperside of pixel electrode 11 is similar to that shown in FIG. 2.

In this embodiment, effects similar to those in the first embodiment canbe attained.

A dummy gate signal line and a dummy pixel electrode, which areapplicable to both the first and second embodiments, are described inthe following.

To apply the present invention, a gate signal line of an (n−1)th columnis needed to form Cs on Gate for a pixel electrode of an nth column.Therefore, a gate signal line of a 0th column is needed to form Cs onGate for a pixel electrode of a first column. The gate signal line ofthe 0th column is not necessarily a signal line to provide a signal tothe gate of a TFT element for driving a pixel electrode. It is a signalline arranged only to form Cs on Gate for a pixel electrode of the firstcolumn. It can be referred to as a kind of “dummy gate signal line” froma relative location thereof. An example thereof is shown in FIG. 5. G0is the dummy gate signal line.

In the liquid crystal display device including such dummy gate signalline, each of a plurality of pixel electrodes includes correspondingauxiliary electrode and TFT element, and it can be said that one of thegroup of gate signal lines located in an end position of one side (thedummy gate signal line) has a portion forming a capacitor by overlappingwith the auxiliary electrode, and is not connected to any of TFTelement.

To drive the liquid crystal display device having such construction,when the group of gate signal lines are indicated with G0, G1, G2, . . ., Gp in order of arrangement position, a line of pixels (generally ahorizontal line) along the gate signal line is selected one by oneregarding to G1 to Gp in this order, a potential corresponding tocontent of a picture to be displayed is provided to each pixel electrodearranged in the selected one line from the source signal line for acertain time, and a constant potential is provided to the pixelelectrodes belonging to all of not-selected lines. After a selection ofGp, the steps are repeated from G1, and during these steps, the constantpotential is continuously provided to G0. That is, as shown in FIG. 6,when a line corresponding to general gate signal line Gn other than G0is noted, a timing of scanning comes in a constant cycle generallycalled “1V” (a cycle of vertical synchronization, which is also referredto as a “vertical period”), and a potential corresponding to content ofa picture is applied to each pixel electrode belonging to this line fromthe source signal line during a time called “1H” (a cycle of horizontalsynchronization, which is also referred to as a “horizontal period”). Ineach of FIGS. 6 and 7, a horizontal axis indicates an elapsed time and avertical axis indicates a voltage. After time 1H in gate signal line Gnelapsed, an object of application is shifted to a line corresponding togate signal line Gn+1. As shown in FIG. 7, the potential correspondingto the content of picture is also applied to each pixel electrodebelonging to a line corresponding to gate signal line G1 in a constantcycle, as part of a cycle of this scanning. To dummy gate signal lineG0, however, the potential for displaying picture is not applied, and aconstant potential corresponding to non-display of the picture iscontinuously applied.

A “dummy pixel electrode” may be arranged in addition to the dummy gatesignal line as described above. FIG. 8 shows a structure of a regionnear the dummy pixel electrode in such example. A region between gatesignal lines G0 and G(−1) is a dummy pixel region in which a dummy pixelelectrode 11 d is arranged. An auxiliary electrode 13 d arranged on alower side of pixel electrode 11 d so as to have the same potential asdummy pixel electrode 11 d is also a dummy electrode. Actually, allpixel electrodes of a column laterally extending from FIG. 8 correspondto dummy pixel electrodes. Thus, it can be said that there is a “dummypixel electrode column”.

In the liquid crystal display device including such dummy pixelelectrodes, each pixel electrode includes corresponding auxiliaryelectrode and TFT element, and it can be said that a pixel electrodelocated between two of the group of gate signal lines in first andsecond positions from an end of one side, that is to say, a dummyelectrode is not for displaying.

To drive the liquid crystal display device having such construction,when a column of the pixel electrodes located between two of the groupof the gate signal lines in first and second positions from an end ofone side is made to be a dummy pixel electrode column and the othercolumns of the pixel electrodes are made to be active pixel electrodecolumns, a column is selected one by one in order of arrangementposition over all of the active pixel electrode columns, a potentialcorresponding to content of a picture to be displayed is provided to thepixel electrodes of the selected one column, a constant potential isprovided to the pixel electrodes of the other columns, and such scanningis repeated from one end to the other end of an arrangement of activepixel electrode columns, while the constant potential is continuouslyprovided to the pixel electrodes in the dummy pixel electrode column.

The dummy pixel electrode may be covered with the aforementioned blackmatrix to avoid an effect of the dummy pixel electrode on display.

A further function attained when the auxiliary capacity is increasedaccording to the present invention will now be described.

Hereinafter, CsC represents an auxiliary capacity with Cs on Common, CsGrepresents an auxiliary capacity with Cs on Gate, Clc represents anliquid crystal capacity, and Cgd represents a parasitic capacity betweenthe gate and drain of TFT element. Vg_(p-p) represents an amplitude(peak to peak) of a gate voltage.

A potential difference resulting from dropping of a potential of thepixel electrode to a negative side by an effect of a gate signal with anexistence of Cgd is hereinafter referred to as a “drop voltage”.Auxiliary capacity Cs has a function of minimizing the drop voltage ΔV.Generally, drop voltage ΔV can be expressed as follows.ΔIV=Vg_(p-p)×α  expression 1

where

$\begin{matrix}{\alpha = \frac{Cgd}{{Clc} + {Cgd} + {Cs}}} & {{expression}\mspace{14mu} 2}\end{matrix}$

Therefore, as auxiliary capacity Cs becomes larger, ΔV becomes smaller.

In addition, the following expressions can be led from expression 2.

$\begin{matrix}{{\alpha\left( {{Cs}\mspace{14mu}{on}\mspace{14mu}{Common}} \right)} = \frac{Cgd}{{Clc} + {Cgd} + {CsC}}} & {{expression}\mspace{14mu} 3} \\{{\alpha\left( {{Cs}\mspace{14mu}{on}\mspace{14mu}{Gate}} \right)} = \frac{Cgd}{{Clc} + {Cgd} + {CsG}}} & {{expression}\mspace{14mu} 4} \\{{\alpha\left( {{{{Cs}\mspace{14mu}{on}\mspace{14mu}{Common}}\;\&}\mspace{14mu}{Cs}\mspace{14mu}{on}\mspace{14mu}{Gate}} \right)} =} & {{expression}\mspace{14mu} 5} \\{\mspace{140mu}\frac{Cgd}{{Clc} + {Cgd} + {CsC} + {CsG}}} & \;\end{matrix}$

where α(Cs on Common), α(Cs on Gate) and α(Cs on Common & Cs on Gate)respectively represent α values in a structure only with Cs on Common,in a structure only with Cs on Gate and in a structure with combined Cson Common and Cs on Gate in one pixel electrode according to the presentinvention.

From expressions 2, 3 and 4, the following relations are held.α(Cs on Common & Cs on Gate)<α(Cs on Common)  expression 6α(Cs on Common & Cs on Gate)<α(Cs on Gate)  expression 7

In the present invention using combined Cs on Common and Cs on Gate inone pixel, the α value becomes smaller than that in the conventionalstructure only with Cs on Common or Cs on Gate. It is apparent withconsideration of expression 1 that the present invention can make ΔVsmaller and enhance performance of pixel drive.

It is to be noted that, though TFT is illustrated as the switchingelement in the aforementioned embodiments, this is not a limitation, andan MIM, a diode or a thyristor may also be used.

Third Embodiment

A liquid crystal display device in a third embodiment according to thepresent invention will now be described. With the liquid crystal displaydevice as described in the first or second embodiment, which is a typeof using combined Cs on Common and Cs on Gate in one pixel (hereinafterreferred to as a “combined type”), an optimal state is not alwaysobtained with simple combination, and there is a more preferableconstruction of the combined type. An optimal construction of thecombined type is described from the third embodiment.

A flicker is noted here as one of malfunctions occur in a product. Theflicker is a phenomenon of flickering of a screen. The flicker isgenerated in a liquid crystal display device on a principle as describedin the following.

As shown in FIG. 9, a pixel electrode usually displays an image byalternately receiving a signal 81 which is positive to a potential of anopposed electrode, that is, an opposed potential V0, and a signal 82which is negative. Potential differences with opposed potential V0should be equalized to uniformly display the image during bothapplications of positive and negative signals. Herein, a potentialgenerated in the pixel electrode is not a source potential of TFTelement itself, but it is a potential obtained by subtracting dropvoltage ΔV from the source potential. Therefore, the potential of theopposed electrode and the source potential are set to allow a resultingequal absolute value of potential differences between the pixelelectrode and the opposed electrode for both applications of positiveand negative signals, in consideration of a decrement of the potentialby drop voltage ΔV.

In reality, however, the potential generated in the pixel electrode isnot equal to the potential obtained by subtracting drop voltage ΔV fromthe source potential, but it is incremented again by a drop relaxationvoltage ΔVc (described in detail below). A value of drop relaxationvoltage ΔVc is determined depending on a distance of wiring from a gatedriver to the pixel electrode. As shown in FIG. 10, a gate driver 85 anda source driver 86 are respectively arranged on the outsides oflongitudinal and lateral sides of a screen 87. In a situation of aso-called single-bank drive, that is, when gate driver 85 is arrangedonly on the outside of a left side of the screen as shown in FIG. 10, adistance of wiring from gate driver 85 widely differs depending on aposition of the pixel electrode. Thus, the value of drop relaxationvoltage ΔVc varies depending on a position of the pixel electrode on thescreen.

The value of drop relaxation voltage ΔVc varies with a region on thescreen. Therefore, a degree of an increment of drop relaxation voltageΔVc in the potential of the pixel electrode differs with a differentregion on the screen, and thus in some regions on the screen, potentialdifferences with the opposed electrode will not be equal forapplications of positive and negative signals; as shown in FIG. 11. Suchshift in the potential differences with the opposed electrode isreferred to as an “opposed voltage shift”. The “opposed voltage shift”is more precisely defined as a difference between maximal and minimalvalues of drop relaxation voltage ΔVc throughout the screen. When theopposed voltage shift becomes large to some degree, it is recognized asa flicker by a user.

Herein, Vgh represents a potential of a High signal of a gate signalprovided to the gate electrode of TFT element, and Vgl represents apotential of a Low signal. Vth represents a potential difference neededto maintain an ON state of TFT, that is, a TFT threshold value. Apotential realized by potential difference Vth is represented as vTFT.

When the potential of the gate signal is switched from Vgh to Vgl, thepotential of the pixel electrode decreases by an effect of parasiticcapacity Cgd between the gate and drain. In theory, however, thepotential becomes stable after decreased to a certain degree. A voltagecorresponding to a decrement of this decrease is drop voltage ΔV, whichis also described in the second embodiment.

A time when TFT element is switched from an ON state to an OFF state isconsidered. During the ON state, potential Vgh is applied to the gateelectrode of the TFT element as the gate signal. When the gate signal isswitched from Vgh to Vgl to switch TFT element to the OFF state, thepotential of the gate electrode does not immediately change from Vgh toVgl. In reality, as shown in FIG. 12, the potential decreases toward Vglin a curve over a certain time. In FIG. 12, a horizontal axis indicatesan elapsed time and a vertical axis indicates an actual potential of thegate electrode.

While the actual potential of the gate electrode is decreasing towardVgl, TFT element is actually switched to the OFF state when thepotential difference between the gate electrode and the source becomeslower than potential vTFT as TFT threshold value Vth. Thus, there is adifference between a time t2 when the gate signal provided to TFTelement is switched to Vgl and a time toff when TFT element is actuallyset to the OFF state. Length of this time difference is represented astTFToff.

Though TFT element should be set to the OFF state in a period from timet2 to time toff in theory, it is still in the ON state in reality andthus charging is performed. Though the potential of the pixel electrodeis decreasing in the period from time t2 to time toff, charging isperformed on the other hand. In theory, a final stable value of thepotential of the pixel electrode should be a value decremented by dropvoltage ΔV. In reality, however, it is only decremented by ΔV−ΔVcbecause of the charging performed during the period from time t2 to timetoff. A component ΔVc of increment in the potential drop is referred toas a “drop relaxation voltage”.

Length tTFToff of a charging time is expressed as the followingexpression 8.

$\begin{matrix}\begin{matrix}{{tTFToff} = {{toff} - {t2}}} \\{= {{- {Rg}} \times \left( {{Cg} + {{Nm}/\left( {{1/{Csg}} +} \right.}} \right.}} \\{\left. \left. {1/\left( {{Clc} + {Cscom}} \right)} \right) \right) \times} \\{\ln\left( {{{Voff}/{Vgh}} - {Vgl}} \right)}\end{matrix} & {{expression}\mspace{14mu} 8}\end{matrix}$

Herein, each of indications represents a meaning as follows.

Nm: a number of pixels in a horizontal direction

Rg: a resistance for one gate wiring

Cg: a capacity for one gate wiring (a capacity on an assumption that itis not connected to each pixel electrode)

Csg: a capacity of Cs on Gate per one pixel

Cscom: a capacity of Cs on Common per one pixel

Clc: a liquid crystal capacity per one pixel

Voff: a potential difference of a gate electrode to Vgl at switching ofON/OFF state of TFT elementVoff=Vγ+vTFToff−Vgl

Vγ: a source potential determined depending on a gradation

FIG. 13 shows relations of connections of Csg, Clc and Cscom to TFTelement in one pixel.

A resistance Ron at a time when TFT element is set to the ON state isexpressed as the following expression 9.Ron=(ton−t2)/Cpixl×ln((Vγ−Vcharge)Vγ)  expression 9

ton: a time when TFT element is actually set to the ON state

Cpixl: a total capacity relating to one pixelCpixl=Clc+Cscom+Csg+Cgd

Cgd: a parasitic capacity between the gate and drain per one pixel

Vcharge: a voltage actually charged in the liquid crystal

Drop relaxation voltage ΔVc generated resulting from obtuseness of awaveform when the gate signal is set to the OFF state can be expressedas the following expression 10.ΔVc=ΔV/(Ron·Cpixl)·[t+Rg·Cgi·exp(−t/(Rg·Cgi))]₀ ^(tTFoff)  expression 10

Herein, Cgi=Cg+Nm/(1/Csg+1/(Clc+Cscom)). In expression 10, a portion []₀ ^(tTFoff) means an integral in regard to t from 0 to tTFToff.ΔV=Cgd/Cpixl·(Vgh−Vgl)

A minimal value of the opposed voltage shift required to recognize theflicker will now be described.

As a precondition for a simulation, it is assumed that an appliedvoltage of a liquid crystal is up to 4 V, and 64 levels of halftone aredisplayed within the range. It is assumed that a difference betweenmaximal and minimal values of luminance is 250 cd/m². A minimal value ofa luminance difference with the opposed voltage shift to recognize theflicker, which value is obtained by an experiment, is 4 cd/m².4V×(4 cd/m²≈250 cd/m²)≈0.06V

Therefore, the flicker can be recognized when the opposed voltage shiftof about 0.06 V or larger is generated.

To avoid generation of recognizable flicker in the single-bank drive,drop relaxation voltage ΔVc expressed as expression 10 should be 0.06 Vor lower.

A model as shown in FIG. 14 was constructed, and a simulation wasperformed to examine a degree of generation of the opposed voltageshift. The model shown in FIG. 14 was formed with the circuitconstruction of FIG. 13 considering a resistance of wiring or the like.Though an actual screen of an XGA (extended Graphic Array) standard has1024×3 colors=3072 pixel electrodes arranged in a lateral direction, inthe simulation, a number of pixel electrodes arranged in a lateraldirection was set to 10, which corresponds to approximately 1/300of anactual number. Besides such simplification, however, a resistance valueand a capacity value per one pixel were set to 300 times the values inone pixel in reality to match a total resistance value and a totalcapacity value for one row arranged in a lateral direction with actualvalues.

Each of small rectangles shown in FIG. 14 indicates a source of apotential. Variables in FIG. 14 represent meanings as follows.

Csg: a Cs-on-Gate capacity

Cscom: a Cs-on-Common capacity

Clc: a liquid crystal capacity

Rcs1, Rcs2: resistances of auxiliary capacity wiring

Rg1, Rg2: resistances of a left side and a right side, respectively, ofgate wiring per one pixel

Roff: a drain electrode leak component

Cg: a capacity of gate wiring, which capacity is not connected toindividual pixel electrode

Cgd: a parasitic capacity between the gate and drain

A simulation was performed in this model. A screen of XGA standardhaving a size of 15 inches is assumed. The simulation was performed forthree structures, that is, a structure only with Cs on Gate, a structureonly with Cs on Common and a structure of the combined type. As shown inFIG. 14, Cscom was fixed to 45 pF. Csg was varied within a range from 0to 90 pF, and the simulation was respectively performed. A result isshown in FIG. 15. In FIG. 15, the minimal value of the opposed voltageshift to recognize the flicker (hereinafter referred to as a “flickerrecognition threshold value”) is indicated with a straight line. Theflicker recognition threshold value is a value slightly larger than 0.06V.

The opposed voltage shift was large in the structure only with Cs onGate, and the value thereof was larger than the flicker recognitionthreshold value even when Csg was set to as a large value as 90 pF. Theopposed voltage shift also became larger than the flicker recognitionthreshold value in the structure only with Cs on Common. That is, theflicker was recognizable in both structures, only with Cs on Gate andonly with Cs on Common.

In contrast, the opposed voltage shift became smaller than the flickerrecognition threshold value in the combined type. That is, a statewithout generation of recognizable flicker could be made.

Though Cscom was fixed to 45 pF in FIG. 15, a liquid crystal displaydevice without recognizable flicker as shown in FIG. 15 can be obtainedprovided that Cscom is 45 pF or higher. The state of Cscom being 45 pFmeans that the auxiliary capacity wiring has a width Wcscom of 10 μm.When width Wcscom of the auxiliary capacity wiring was made smaller than10 μm, the opposed voltage shift could not reliably be made smaller thanthe flicker recognition threshold value. Therefore, a preferablecondition to avoid generation of the flicker is to set the width of theauxiliary capacity wiring to 10 μm or larger.

Thus, the liquid crystal display device in the third embodimentaccording to the present invention is the liquid crystal display devicehaving a width of the auxiliary capacity wiring of 10 μm or larger.

Increase in the width of the auxiliary capacity wiring, however, causesdecrease in an aperture ratio, and thus it is preferable to set thewidth of the auxiliary capacity wiring to 10 μm to avoid the decrease inthe aperture ratio. Therefore, in the liquid crystal display device inthis embodiment, the auxiliary capacity wiring preferably has a width ofapproximately 10 μm. Other constructions are similar to those describedin the first or second embodiment.

With the liquid crystal display device satisfying this condition,generation of recognizable flicker can be suppressed.

Fourth Embodiment

In the simulation in the model shown in FIG. 14, the screen had a sizeof 15 inches and Cscom was 45 pF. When other screen size is assumed,however, a minimal value of capacity that should be held as Cscomvaries. Capacity Cscom preferably satisfies the following expression.Cscom≧(S/15)×45 pFwhere S represents a size of the screen in inches. Capacity Cscom is acapacity of a portion of the auxiliary electrode forming a capacitor byoverlapping with the auxiliary capacity wiring.

Thus, a first example of a liquid crystal display device in a fourthembodiment according to the present invention is a liquid crystaldisplay device which satisfies the following expression. Otherconstructions are similar to those described in the first or secondembodiment.Cscom≧(S/15)×45 pF

Width Wcscom of the auxiliary capacity wiring preferably satisfies thefollowing expression.Wcscom≧10 μm×6.9/∈2

In this expression, the number 6.9 comes from a value 6.9 of relativepermittivity ∈1 which was used to calculate a capacity value of Cscom inthe simulation. In addition, ∈2 represents relative permittivityobtained when a capacity of Cscom is formed in a liquid crystal displaydevice having each inch size.

Thus, a second example of the liquid crystal display device in thefourth embodiment according to the present invention is the liquidcrystal display device which satisfies the following expression. Otherconstructions are similar to those described in the first or secondembodiment.Wcscom≧10 μm×6.9/∈2

With the liquid crystal display device satisfying the conditiondescribed in the first or second example, generation of recognizableflicker can be suppressed.

Fifth Embodiment

In the above-described simulation, Rg1 and Rg2 were respectively set to0.05 kΩ. Thus, a resistance value of the gate wiring per one pixel isRg1+Rg2=0.10 kΩ. To avoid generation of a flicker, a value of Rg1+Rg2must be made equal to or smaller than this value. As it is assumed inthis simulation that ten pixels are arranged in a lateral row on thescreen, a resistance value per one gate wiring (also referred to as a“gate bus line”), which corresponds to the second signal line in thefirst embodiment, is 0.10 kΩ×10=1 kΩ. Therefore, to avoid generation ofa flicker, the resistance value per one second signal line is preferablyequal to or lower than 1 kΩ. The resistance value per one gate wiring asthe second signal line equal to or lower than 1 kΩ can be attained byforming the gate wiring with aluminum, chromium, copper, or the like.

Thus, a liquid crystal display device in a fifth embodiment according tothe present invention is the liquid crystal display device having aresistance value per one second signal line equal to or lower than 1 kΩ.Other constructions are similar to those described in the first orsecond embodiment.

Though each of the preferable conditions described in the third to fifthembodiments is efficient to a certain extent by itself, it is morepreferable to concurrently satisfy two or more of the conditions,because the effect of suppressing flicker can be obtained more reliably.

Sixth Embodiment

Expressions 8 and 10 are premised on a single-bank drive as shown inFIG. 10. A situation of a dual-bank drive as shown in FIG. 16 will nowbe considered. In FIG. 16, gate drivers 85 a and 85 b are arranged onthe outside of left and right sides of a screen, and wirings areextending from both left and right sides for pixels within screen 87.Each of gate drivers 85 a, 85 b covers and drives each half of pixelelectrodes arranged within screen 87. A dual-bank drive of N pixels,where N represents a number of pixels arranged from left to right, isequivalent to a single-bank drive of N/2 pixels.

With reference to expression 8 which expresses time difference tTFToffduring a switching of TFT element to the OFF state in the single-bankdrive, a time difference tTFToffb similarly generated in the dual-bankdrive has a relation with time difference tTFToff of the single-bankdrive as follows.tTFToffb=tTFToff/4

In addition, as both Rg and Cg in the dual-bank drive are halves ofthose in the single-bank drive, drop relaxation voltage ΔVc can beexpressed as the following expression 11.ΔVc=ΔV/(Ron·Cpixl)·[t+(Rg·Cgi/4)·exp(−t/(Rg·Cgi/4))]₀^(tTFToff)  expression 11

To avoid the generation of recognizable flicker in the dual-bank drive,drop relaxation voltage ΔVc expressed as expression 11 should be 0.06 Vor lower. Other constructions are similar to those described in thefirst or second embodiment.

As a load resulting from a resistance of gate wiring also becomes halfin the dual-bank drive, a minimal value of resistance is twice the valuein the single-bank drive. Therefore, the resistance value per one gatewiring, that is, second signal line is preferably equal to or lower than2 kΩ. For this condition, other constructions are also similar to thosedescribed in the first or second embodiment.

With the liquid crystal display device satisfying either of theseconditions, generation of recognizable flicker can be suppressed. Theliquid crystal display device satisfying both of the preferableconditions described in this embodiment is more preferable, because thegeneration of recognizable flicker can be suppressed more reliably.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the spiritand scope of the present invention being limited only by the terms ofthe appended claims.

1. A liquid crystal display device, comprising: a group of first signallines arranged in parallel; a group of second signal lines and a groupof auxiliary capacity wirings alternately arranged one by one inparallel so as to intersect with the group of said first signal lines; aplurality of switching elements arranged corresponding to intersectionpoints of said first signal lines and said second signal lines; aplurality of auxiliary electrodes connected to said plurality ofswitching elements; and a pixel electrode formed on said auxiliaryelectrode and electrically connected to said auxiliary electrode;wherein said auxiliary electrode has a portion forming a capacitor byoverlapping with said auxiliary capacity wiring and a portion forming acapacitor by overlapping with said second signal line, and the pixelelectrode and the auxiliary electrode are laid on each other with atransparent insulation film interposed therebetween.
 2. A liquid crystaldisplay device, comprising: a group of first signal lines arranged inparallel; a group of second signal lines and a group of auxiliarycapacity wirings alternately arranged one by one in parallel so as tointersect with the group of said first signal lines; a plurality ofpixel electrodes arranged in a pixel region defined as each regionenclosed with two of the group of said first signal lines which areadjacent with each other and two of the group of said second signallines which are adjacent with each other; an auxiliary electrodeconnected to each of said pixel electrodes; and a thin film transistorcorresponding to each of said pixel electrodes; wherein said thin filmtransistor has one side of a source and a drain connected to said firstsignal line, the other side connected to said auxiliary electrode, and agate side connected to said second signal line, said auxiliary electrodehas a portion forming a capacitor by overlapping with said auxiliarycapacity wiring and a portion forming a capacitor by overlapping withsaid second signal line, and the pixel electrode and the auxiliaryelectrode are laid on each other with a transparent insulation filminterposed therebetween.
 3. The liquid crystal display device accordingto claim 2, wherein each of said plurality of pixel electrodes includescorresponding said auxiliary electrode and said thin film transistor,and one of the group of said second signal lines located in an endposition of one side has a portion forming a capacitor by overlappingwith said auxiliary electrode and is not connected to any of said thinfilm transistor.
 4. The liquid crystal display device according to claim2, wherein each of said pixel electrodes includes corresponding saidauxiliary electrode and said thin film transistor, and wherein saidpixel electrode located between two of the group of said second signallines in first and second positions from an end of one side does nothave a pixel electrode applied thereto.
 5. The liquid crystal displaydevice according to claim 1, wherein when a group of second signal linesare indicated with G0, G1, G2, . . . , Gp in order of arrangementposition, a picture signal to be displayed is successively applied to G1to Gp in one vertical period, and a constant potential is applied to G0.6. The liquid crystal display device according to claim 1, wherein whena column of said pixel electrodes located between two of the group ofsaid second signal lines in first and second positions from an end ofone side is made to be a dummy pixel electrode column and the othercolumns of said pixel electrodes are made to be active pixel electrodecolumns, a column is selected one by one in order of arrangementposition over all of the active pixel electrode columns, a potentialcorresponding to content of a picture to be displayed is provided to aselected one column of said pixel electrodes, a constant potential isprovided to the other columns of said pixel electrodes, and suchscanning is repeated from one end to the other end of an arrangement ofthe active pixel electrode columns, while continuously providing saidconstant potential to said dummy pixel electrode.
 7. A liquid crystaldisplay device, comprising: a group of first signal lines arranged inparallel; a group of second signal lines and a group of auxiliarycapacity wirings alternately arranged one by one in parallel so as tointersect with the group of said first signal lines; a plurality ofswitching elements arranged corresponding to intersection points of saidfirst signal lines and said second signal lines; a plurality ofauxiliary electrodes connected to said plurality of switching elements;and a pixel electrode formed on said auxiliary electrode andelectrically connected to said auxiliary electrode; wherein saidauxiliary electrode has a portion forming a capacitor by overlappingwith said auxiliary capacity wiring and a portion forming a capacitor byoverlapping with said second signal line, and a width of said auxiliarycapacity wiring is 10 μm or larger.
 8. The liquid crystal display deviceaccording to claim 1, wherein a capacity Cscom of a portion of saidauxiliary electrode forming a capacitor by overlapping with saidauxiliary capacity wiring satisfiesCscom≧(S/15)×45 pF where S represents a size of a screen in inches. 9.The liquid crystal display device according to claim 1, wherein a widthWcscom of said auxiliary capacity wiring satisfiesWcscom≧10 μm×6.9/∈2 where ∈2 represents relative permittivity of acapacitor formed by overlapping of said auxiliary electrode with saidauxiliary capacity wiring.
 10. A liquid crystal display device,comprising: a group of first signal lines arranged in parallel; a groupof second signal lines and a group of auxiliary capacity wiringsalternately arranged one by one in parallel so as to intersect with thegroup of said first signal lines; a plurality of switching elementsarranged corresponding to intersection points of said first signal linesand said second signal lines; a plurality of auxiliary electrodesconnected to said plurality of switching elements; and a pixel electrodeformed on said auxiliary electrode and electrically connected to saidauxiliary electrode; wherein said auxiliary electrode has a portionforming a capacitor by overlapping with said auxiliary capacity wiringand a portion forming a capacitor by overlapping with said second signalline, and said liquid crystal display device is a single-bank drive, andhas a resistance value per one said second signal line of 1 kΩ orsmaller.
 11. The liquid crystal display device according to claim 1,wherein said liquid crystal display device is a single-bank drive, andhas a drop relaxation voltageΔVc=ΔV/(Ron·Cpixl)·[t+Rg·Cg·exp(−t/(Rg·Cg))]₀ ^(tTFToff) of 0.06 V orsmaller.
 12. A liquid crystal display device, comprising: a group offirst signal lines arranged in parallel; a group of second signal linesand a group of auxiliary capacity wirings alternately arranged one byone in parallel so as to intersect with the group of said first signallines; a plurality of switching elements arranged corresponding tointersection points of said first signal lines and said second signallines; a plurality of auxiliary electrodes connected to said pluralityof switching elements; and a pixel electrode formed on said auxiliaryelectrode and electrically connected to said auxiliary electrode;wherein said auxiliary electrode has a portion forming a capacitor byoverlapping with said auxiliary capacity wiring and a portion forming acapacitor by overlapping with said second signal line, and said liquidcrystal display device is a dual-bank drive, and has a resistance valueper one said second signal line of 2 kΩ or smaller.
 13. The liquidcrystal display device according to claim 1, wherein said liquid crystaldisplay device is a dual-bank drive, and has a drop relaxation voltageΔVc=ΔV/(Ron·Cpixl)·[t+(Rg·Cg/4)·exp(−t/(Rg·Cg/4))]_(tTFToff) of 0.06 Vor smaller.
 14. The liquid crystal display device according to claim 2,wherein a width of said auxiliary capacity wiring is 10 μm or larger.15. The liquid crystal display device according to claim 2, wherein acapacity Cscom of a portion of said auxiliary electrode forming acapacitor by overlapping with said auxiliary capacity wiring satisfiesCscom≧(S/15)×45 pF where S represents a size of a screen in inches. 16.The liquid crystal display device according to claim 2, wherein a widthWcscom of said auxiliary capacity wiring satisfiesWcscom≧10 μm×6.9/∈2 where ∈2 represents relative permittivity of acapacitor formed by overlapping of said auxiliary electrode with saidauxiliary capacity wiring.
 17. The liquid crystal display deviceaccording to claim 2, wherein said liquid crystal display device is asingle-bank drive, and has a resistance value per one said second signalline of 1 kΩ or smaller.
 18. The liquid crystal display device accordingto claim 2, wherein said liquid crystal display device is a single-bankdrive, and has a drop relaxation voltageΔVc=ΔV/(Ron·Cpixl)·[t+Rg·Cg·exp(−t/(Rg·Cg))]₀ ^(tTFToff) of 0.06 V orsmaller.
 19. The liquid crystal display device according to claim 2,wherein said liquid crystal display device is a dual-bank drive, and hasa resistance value per one said second signal line of 2 kΩ or smaller.20. The liquid crystal display device according to claim 2, wherein saidliquid crystal display device is a dual-bank drive, and has a droprelaxation voltage ΔVc=ΔV/(Ron·Cpixl)·[t+(Rg·Cg/4)·exp(−t/(Rg·Cg/4))]₀^(tTFToff) of 0.06 V or smaller.
 21. A liquid crystal display device,comprising: a group of first signal lines arranged in parallel; a groupof second signal lines and a group of auxiliary capacity wiringsalternately arranged one by one in parallel so as to intersect with thegroup of said first signal lines; a plurality of pixel electrodesarranged in a pixel region defined as each region enclosed with two ofthe group of said first signal lines which are adjacent with each otherand two of the group of said second signal lines which are adjacent witheach other; an auxiliary electrode connected to each of said pixelelectrodes; and a thin film transistor corresponding to each of saidpixel electrodes; wherein said thin film transistor has one side of asource and a drain connected to said first signal line, the other sideconnected to said auxiliary electrode, and a gate side connected to saidsecond signal line, said auxiliary electrode has a portion forming acapacitor by overlapping with said auxiliary capacity wiring and aportion forming a capacitor by overlapping with said second signal line,each of said pixel electrodes includes corresponding said auxiliaryelectrode and said thin film transistor, and said pixel electrodelocated between two of the group of said second signal lines in firstand second positions from an end of one side does not have a pixelelectrode applied thereto.
 22. A liquid crystal display device,comprising: a group of first signal lines arranged in parallel; a groupof second signal lines and a group of auxiliary capacity wiringsalternately arranged one by one in parallel so as to intersect with thegroup of said first signal lines; a plurality of switching elementsarranged corresponding to intersection points of said first signal linesand said second signal lines; a plurality of auxiliary electrodesconnected to said plurality of switching elements; and a pixel electrodeformed on said auxiliary electrode and electrically connected to saidauxiliary electrode; wherein said auxiliary electrode has a portionforming a capacitor by overlapping with said auxiliary capacity wiringand a portion forming a capacitor by overlapping with said second signalline, and when a group of second signal lines are indicated with G0, G1,G2, . . . , Gp in order of arrangement position, a picture signal to bedisplayed is successively applied to G1 to Gp in one vertical period,and a constant potential is applied to G0.
 23. A liquid crystal displaydevice, comprising: a group of first signal lines arranged in parallel;a group of second signal lines and a group of auxiliary capacity wiringsalternately arranged one by one in parallel so as to intersect with thegroup of said first signal lines; a plurality of switching elementsarranged corresponding to intersection points of said first signal linesand said second signal lines; a plurality of auxiliary electrodesconnected to said plurality of switching elements; and a pixel electrodeformed on said auxiliary electrode and electrically connected to saidauxiliary electrode; wherein said auxiliary electrode has a portionforming a capacitor by overlapping with said auxiliary capacity wiringand a portion forming a capacitor by overlapping with said second signalline, and when a column of said pixel electrodes located between two ofthe group of said second signal lines in first and second positions froman end of one side is made to be a dummy pixel electrode column and theother columns of said pixel electrodes are made to be active pixelelectrode columns, a column is selected one by one in order ofarrangement position over all of the active pixel electrode columns, apotential corresponding to content of a picture to be displayed isprovided to a selected one column of said pixel electrodes, a constantpotential is provided to the other columns of said pixel electrodes, andsuch scanning is repeated from one end to the other end of anarrangement of the active pixel electrode columns, while continuouslyproviding said constant potential to said dummy pixel electrode.